style(ui): lists icons, section headers, active state

- Add central icon library (Icon.Sun/Activity/Star/Calendar/Eye/Inbox/Folder/Search/Plus/MoreHorizontal/GitBranch/Copy/Trash/Sort/X/Check) to IslandStyles.axaml
- Add list-section-label, search-wrap, kbd, new-list-btn, avatar-circle styles
- Add UpperCaseConverter, IconKeyConverter, DotBrushConverter; register in App.axaml
- Expose SmartLists / UserLists filtered collections from ListsIslandViewModel
- Add DotColorKey (Moss/Peat/Sage rotation) and UserInitials/UserName/MachineName props

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ClaudeDo.App/App.axaml

@@ -15,6 +15,9 @@
             <converters:NotNullToBoolConverter x:Key="NotNullToBool"/>
             <converters:StrikeIfTrueConverter  x:Key="StrikeIfTrue"/>
             <converters:EqStatusConverter      x:Key="EqStatus"/>
+            <converters:UpperCaseConverter     x:Key="UpperCase"/>
+            <converters:IconKeyConverter       x:Key="IconKey"/>
+            <converters:DotBrushConverter      x:Key="DotBrush"/>
 
         </ResourceDictionary>
     </Application.Resources>